Returning to the origins

Researchers are developing a new method for studying a rare genetic disease that could serve as model and facilitate research on other problems affecting stem cells.

By Elton Alisson

Agência FAPESP – Research on diseases that affect stem cells have gained a new perspective. A group of researchers from the Stanford University Medical School in the United States, including a Brazilian, has developed a new method for studying a rare genetic disease in vitro. The model could serve to facilitate research on other diseases caused by the poor functioning of the cellular system.

The study was described in an article published in the May 22 edition of Nature, authored by São Paulo researcher Luís Francisco Zirnberger Batista. The researcher studied biomedical sciences at the Universidade de São Paulo (USP) with a scholarship from FAPESP, and has been completing post-doctoral research at the U.S. university since 2008.

Through the study, Batista and the U.S. researchers developed induced pluripotent stem cells (iPS) from patients with dyskeratosis congenita – a rare disease caused by the rapid  shortening of long repetitive sequences of DNA located on the extremities of chromosomes (the telomeres)--to study stem cells.

In analyzing the iPS, which are morphologically identical to human stem cells, the researchers managed to demonstrate for the first time how the disease functions. The disease varies from patient to patient depending on mutations in certain genes of its cells.

Additionally, the researchers observed that the stem cells of patients with dyskeratosis congenita have an extremely reduced renewal capacity. This explains the differences in the severity of the disease, which causes everything from problems of skin pigmentation to bone marrow failure.

“Now with these iPS we have a system to study dyskeratosis congenita in culture. And this can serve as a model for studying other rare diseases that affect stem cells, like Fanconi anemia,” Batista explains to Agência FAPESP.

According to the researcher, patients with dyskeratosis congenita present problems in tissues and bone marrow, where stem cells are in constant division to form specialized cells. And every time these cells split, they lose a piece of the chromosome – in this case telomeres.     
 
As a result, the telomeres of cells in patients with dyskeratosis congenita continue progressively shortening with every cellular division until it reaches point of chromosomal crisis in which the cell stops dividing (senescence), dies or generates genetic instability, which can cause cancer or cellular aging.

“Patients with dyskeratosis congenita have, for example, problems with nails, skin and bone marrow failure, which indicates defects in the capacity of stem cells to maintain stability of these tissues,” explains Batista.

 Some twelve years ago, researchers discovered that the disease is related to mutation of different genes of a complex of enzymes responsible maintaining telomeres, the telomerase. This complex of enzymes is only active, however, in stem or progenitor cells, which also have the capacity to differentiate in a type of specialized cell.

In order to study them, researchers decided to collect skin cells (fibroblastics) from different patients with dyskeratosis congenita and reprogram them to become induced pluripotent stem cells (iPS), following the technique developed by Japanese scientist Shinya Yamanaka in 2006.

“With these cells, we can study a way to increase the efficiency of muted telomerase that patients with dyskeratosis have. And in the study, we showed that with gene therapy it is possible to sidestep the mutation of these genes,” says Batista.

According to researchers, expressing muted telomerase, the telomeres of stem cells in dyskeratosis congenita patients in culture continued progressively shortening over time. And the faster the telomere of cells shortened, the greater the severity of the disease in patients.

Furthermore, the precocious shortening of the telomere caused the cells in the culture to have a short lifespan, an uncommon characteristic for stem cells which are typically capable of renewing themselves in culture for long periods.

“What we saw was that the shortening of cell telomeres in these patients eliminated the autorenewal capacity of these cells and we believe that this occurs with the adult stem cells of these patients. They cannot divide, because the telomeres are very short. This causes the problems that these patients frequently have in their tissues, which need to divide more frequently,” affirmed Batista.

The study is the first to use undifferentiated iPs cells as model for studying disease that affect stem cells.

According to Batista, the studies conducted over the last two years with these cells were aimed at researching different diseases unrelated to stem cells. Furthermore, in these studies, iPs cells were differentiated to analyze specific cells, like nervous system cells.

In the study conducted by the Brazilian and U.S. researchers, they opted not to differentiate the iPS cells of patients with dyskeratosis congenita, without knowing whether they would be able to observe differences.
“We were very happy when we managed to see that the iPs cells are the perfect model for studying dyskeratosis congenita,” he affirmed.

Thomas Cech, the 1999 Nobel Prize winner for Chemistry and professor at the University of Colorado, contributed to the study and is also an author of the article.

In the United States

The Brazilian researcher went to the United States at the end of 2008 after finishing his doctorate at USP’s Institute of Biomedical Sciences where he carried out a study on DNA repair.

Intending to continue researching genetic instability, but now along the lines of DNA repair for telomere maintenance, Batista used the technical reserves from his FAPESP scholarship to participate in a congress in the United States in 2008 in order to make contacts with groups that study the topic.

He chose the laboratory of professor Steven Artandi at the Stanford University School of Medicine, where Batista did his post doctorate under the prestigious Pew Fellowship for the Biomedical Sciences, which he earned in 2009 from the Pew Charitable Trusts Foundation.

The article “Telomere shortening and loss of self-renewal in dyskeratosis congenita induced pluripotent stem cells (doi: 10.1038/nature10084) by Luís Francisco Zirnberger Batista and others can be read by Nature subscribers at: www.nature.com/nature/journal/v474/n7351/full/nature10084.html.